Alternate-current generator.



V. A. PYNN.

ALTERNATE CURRENT GENERATOR.

APPLICATION FILED MAY 23, 1911.

Patented July 21, 1914.

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-UNITED STATES PATENT oFFIoE.

VALERIE 'ALF ED FYNN, or LONDON, ENGLAND.

ALTERNATE-CURRENT GENERATOR.

To (ZZZ whom itmag concern:

Be it known that I, VALiiRE ALFRED EYnN, a' subject of the King ofEngland, residing at London,.England, have invented a certain new anduseful Alternate-Current Generator, of which the following is such afull, clear, and exact description as will enable any one skilled in theart to which it appertains to make anduse the same, refer: ence beinghad to the accompanying drawings, formin part of this specification.

My invention relates to alternate current generators and particularly tomachines generating single phase currents.

It is particularly difficult to construct a ase generator ofconsiderable outmachines of this kind are often required, for instance,for direct coupling to steam turbines and the like. A single phasegenerator of ordinary construction requires careful designing, if areasonable regulation is to be secured, and this difficulty isconsiderably increased in thecase of high speed machines with few poles.

necessitating a large amount of copperon the revolving member andtherefore increasing the difliculty of its mechanical con struction. Itis true that the so-called asynchronous generatorcan be built with smallair gaps but such machines as now constructed are not self-contained andrequire a large synchronous generator or its equivalent to be operatedin parallel with them. The duty of the large synchronous generator is tosupply the stator of the asynchronous generator with the large excitingvolt-amperes it requires and also to determine the periodicity'of thecurrents to be delivered by theasynchronous generator. These factspractically preclude the use of isolated asynchronous generators. Otherdisadvantages attachin to such machines are their inability tosatisfactorily supply low power factor loads and their poor regulatingproperties. Generators of one, two or more phases have also beenproposed in which a commuted winding on the rotor is connected to one ormore of the stator windings by means of brushes and either directly orwith the interposition of one or more transformers. In a single-phaseshunt excited generator of this type the rotor either carries a commutedwinding and a squirrel-cage or the like, or a commuted windingshort-cir- Specification of Letters Patent.

Application filed May 23, 1911.

It becomes necessary in such cases to use very large air gaps, thusPatented July 21, 1914;

Serial No. 628,902.

cuited by means of brushes along an axis about coinciding with that ofthe main stator winding. In either case, the exciting brushes connectedto the main stator winding are disposed along an axis displaced by about9O electrical degrees from the axis.

correspondingly greater number of excitingbrushes. Polyphase shuntalternators of this type have also been proposed with a polyphasearrangement of exciting brushes and both single and polyphasealternators of this type have been compounded by sending into thecommuted rotor winding along the axis of each main stator winding acurrent proportional to that delivered to the mains by the correspondingmain stator winding. In all such alternators the periodicity of thegenerated currents is however not always proportional to the rotorspeed, a fact which entails many undesirable complications. I willdescribe my invention more particularly with reference to a singlephasealternator because the mode of opera- ,alternators of any number ofpoles, of any output and any speed to be designed with small air gaps,to simplify the construction of the revolving member or field magnet, toimprove or control the regulation of such machines, to make themself-contained, and to cause the same to deliver current of aperiodicity strictly proportional to. the speed at which such machinesare driven. I achieve these objects by making the field magnet which, asa rule will be the revolving member, of the rotor type, i. 6., withoutdefined polar projections, by providing this revolving member with awinding shortcircuited along a plurality of axes per pole pair, such asa squirrel cage, and by exciting this field magnet by means of analternating current derived from an external source. In order to makesuch an' excitation efiectively possible I also provide the field magnetwith a commuted winding and send the alternating exciting current intothis commuted winding by Way of a commutator and brushes. I prefer toderive this alternating exciting current from a dynamo electric machinethe armature of which is provided with a commutator and with slip rings.It is necessary for the success of my invention that this exciter bedriven at the same speed as the generator, or at a speed proportional tothat of the latter. If the exciter is driven at the same speed as thegenerator then I prefer to provide both machines with the same number ofpoles. If the exciter is driven at a speed differing from that of thegenerator then I prefer to select for the exciter a number of polesdiffering from that of the generator. Thus, if the exciter is driven attwice the speed of the generator then I would provide said exciter withone-half the number of poles of the generator.

In order to automatically control the regulation of my improvedalternator I insert a series transformer (between the alternatingexciting circuit and the-main or'induced circuit of the generator. Inthe manner above set forth I produce a self-contained alternate currentenerator with small air gap requiring but a small amount of excitingenergy or but a few exciting volt-amperes supplying alternating currentat a definite periodicity absolutely dependent on the speed at which thegenerator is driven and having a very close regulation practicallyindependent of the phase difference between the E. M. F. and currentdelivered by the generator.

My invention will be better understood by reference to the accompanyingdrawings in which Figure 1 is a diagrammatic representation of myimproved generator coupled direct to its exciter, while Fig. 2 moreclearly indicates the electrical connections between the variouswindings on the generator and its exciter.

Referring to Figs. 1 and 2, the field magnet 3 of the generator A andthe armature 24 of the auxiliary generator or exciter B are both keyedto the same shaft 10, and are both wound for the same number of poles.

The generator consists of a revolving member, the mechanicalconstruction of which is identical with that of the rotor of aninduction motor. This rotor carries two independent windings. One ofthese is the commuted winding 4 placed in the bottom of the -rotor slotsand connected to the commutator connected to the slip rings 15-1(3. Theframe 23 of this exciter is of the ordinary construction and is providedwith polar projections which are encrgized by means of the excitingcoils 21. The shunt field winding 21 of the exciter B is connected tothe commutator 22 by way of the brushes 17, 18, a resistance 19adjustable at 25 being included in this shunt exciting circuit for thepurpose of adjusting or regulating the direct current excitation of theexciter B.

The slip rings 1516 of the exciter are con- '11 is connected between theline 26, 27 and the main or generating winding 6 of the alternator A.The transformation ratio of the series transformer 11 can be adjusted bymeans of the movable contact 12.

The mode of operation of this form of my improved generator is somewhatas follows: Suppose the generator and its exciter to be each providedwith two poles and to be coupled direct as shown in Fig. 1. If such aset is driven at 1200 revolutions and the direct current excitingcircuit of the exciter be closed then that machine will deliver to thefield magnet 3 of the generator an alternating current of 20 cycles.Since the brushes 8 and 9 on the commutator. of the generator aredisplaced by 90 electrical de grees from the axis of the main orgenerating winding 6, as shown in Fig. 2, then it will notflbe possiblefor any energy to be transmitted from the exciter B to the maingenerator winding 6 by way of the brushes 8 and 9 nor will it bepossible for any alternating current entering the field magnet by way ofsaid brushes to directly affect the winding 6 in any other way. Thecurrent flowing from 8 to 9, or vice versa will, however afi'ect 6indirectly byproducing along the axis 8, 9 a 20 cycle alternating fluxto which I will refer as the primary alternating flux and which will bereflected along the axis of 6. Briefly, this is brought aboutas follows,by rotation of the squirrel cage winding 5, or its equivalent, in thisprimary fiuxthere Will be generated in 5, an

alternating E. M. F. which will appearalong an axis coinciding with thatof 6. This E. LI. F. to which I will refer as the primary working E.- M.F. will naturally produce a magnetizing current in 5 .this current willlag behind said E. M. F. and will set up a 20 cycle sccondaryorreflected a direction as to oppose all the reactanee E. M. F.s in thealternating current exciting circuit, with the result that the externalE. -M. F. necessary to send the full exciting current through thefieldmagnet 3 of the alternator A becomes very small and does not greatlydiffer from the E. M. F. which would be necessary to send a directcurrent of corresponding value through that same circuit. The smallestvalue of this exciting E. M. F. is reached when the rotor 3 of thealternator A revolves synchronously or nearly so with respect to thenumber of its poles and to the periodicity of the alternating currentsupplied by the exciter B. Thus in the case in which both machines havethe same number of poles the alternating current exciting E. M. F. willbe very near its smallest value when both machines run at the samespeed.

The short-circuited winding 5 carrying along the axis of 6 themagnetizing current already referred to is in reality the primary of atransformer, the secondary of which is constituted by the stator winding6. When the machine is in operation there will appear at the terminalsof .6 an induced alternating E. M. F. to which I will refer as thesecondary working E. M. F. The periodicity of this secondary working E.M. F. is the sameas that of the alternating'E. M. F. generated by theexciter B, its magnitude initially depending on the magnitude of theprimary flux. If translating devices of any kind are connected to thiswinding 6 theywill be supplied with current exactly in the same manneras from an ordinary transformer. The object of the series transformer 11is to increase or decrease the alternating exciting current sent intothe field magnet 3 of the alternator proportionally with the load on thegenerating winding 6, thus increasing or decreasing the primary flux. Ifthe transformer is so connected as to increase said excitation withincreasing load, then the voltage at the terminals of 6 can either bekept fairly constant withvarying loads or can be made to rise withincreasing load, the increased alternate current excitation making upfor the usual drop in voltage to be observed in all generators and duein part-to the ohmic and inductive resistance of the various windingsand in part to what is known as the armature reaction of such machines.

generator very satisfactory even;- without the addition of what may betermed the compounding transformer 11.

Having fully described the n'ature' of my invention and the manner inwhich it is to be performed, I wish it to be understood that I do notlimit myself to the particular embodimentthereof, shown in theaccompanying drawing, but aim in the appended claims to cover all suchmodifications as fall within the scope and the spirit of my invention.

Having fully described my invention, what I claim as new and desire tosecure by Letters Patent of the United States, is:

1. An apparatus for generating alternating current comprising a maingenerator having an induced member provided with a single inducedwinding, and an inducing member provided with a commuted winding and ashort-circuited winding, an auxiliary generator, means for maintaining aconstant ratio between the speeds of the two generators, and means forsupplying single-phase current derived from the auxiliary generator tothe commuted winding of the main generator along an axis displaced byninety electrical degrees from that of the induced winding.

2. An apparatus for generating alternating current comprising a maingenerator having an induced member provided with a single inducedwinding, and an inducing member provided with a commuted winding and ashort-circuitcd winding, an auxiliary generator, means for maintaining aconstant ratio between the speeds of the two generators, means forsupplying singlephase current derived from the auxiliary generator tothe commuted winding of the main generator along an axis displaced byninety electrical degrees from that of the induced winding. and meansexternal to the main generator for electromagnetirally coupling thecommuted winding and the induced winding.

3. An apparatus for generating alternating current comprising a. maingenerator lld ratio between the speeds of the two generators, means forsupplying single-phase cur rent derived from the auxiliary generator tothe commuted winding of the main gen erator along an axis displaced byninety electrical degrees from that. of the induced winding, and aseries transformer interposed between the commuted and the inducedwindings. H

4- An ap aratus for generating alternating current comprising a maingenerator having an induced member provided With a single inducedwinding, and an inducing member provided with a commuted Winding andashort-circuited Winding, a singlephase self-excited auxiliary generatorhaving slip rings, means for maintaining :1 constant ratio between thespeeds of the two generators, and brushes on the commuted Winding of themain generator displaced by ninety electrical degrees from the inducedWinding said brushes being connected to the slip rings of the auxiliarygenerator.

In testimony whereof, I have hereunto set my hand and aflixed my seal inthe presence of the tWo subscribing witnesses.

VALERIE ALFRED FYNN. [1,. s.]

Vitnesses:

\V. A. ALEXANDER, ELIZABETH BAILEY.

